In order to improve recording density of a magnetic recording/reproducing apparatus, development of a magnetic recording medium suitable for high recording density is proceeding.
A magnetic recording medium includes a magnetic layer for recording information, a protective layer made of carbon or the like, and a lubricant layer in this order on a substrate for a magnetic recording medium.
The protective layer protects information recorded on the magnetic layer and enhances slidability of a magnetic head with respect to the magnetic recording medium. However, sufficient durability of the magnetic recording medium cannot be obtained only by providing the protective layer on the magnetic layer.
Therefore, in general, a lubricant is applied to a surface of the protective layer to form a lubricant layer, thereby improving the durability of the magnetic recording medium. By providing the lubricant layer, direct contact between the magnetic head of the magnetic recording/reproducing apparatus and the protective layer can be prevented. In addition, by providing the lubricant layer, frictional force between the magnetic recording medium and the magnetic head sliding on the magnetic recording medium is remarkably reduced. Further, the lubricant layer has a role of preventing corrosion of the magnetic layer or the like of the magnetic recording medium due to impurities invading from the surrounding environment.
Conventionally, as the lubricant used for the lubricant layer of the magnetic recording medium, a perfluoropolyether lubricant and aliphatic hydrocarbon lubricant are used. For example, Patent Document 1 discloses a magnetic recording medium obtained by coating a lubricant of a perfluoroalkyl polyether having a structure of HOCH2—CF2O—(C2F4O)p-(CF2O)q-CH2OH (p, q is an integer) on a protective layer made of carbon or the like.
Patent Document 2 discloses a magnetic recording medium obtained by coating a lubricant of a perfluoroalkylpolyether represented by HOCH2CH(OH)—CH2OCH2CF2O—(C2F4O)p-(CF2O)q-CF2CH2OCH2—CH(OH)CH2OH (p, q is an integer).
Patent Document 3 describes a magnetic recording medium having a lubricant layer containing a mixture of a phosphazene compound and a compound having a perfluorooxyalkylene unit in a specific range of mixing ratios. In addition, Patent Document 3 discloses that the lubricant layer has a high bonding force with a protective layer and a high coverage can be obtained even when the layer thickness of the protective layer is lowered.
Patent Literature 4 discloses a lubricant containing a compound represented by R1—C6H4O—CH2CH(OH)CH2OCH2—R2—CH2—O—R3.    Patent Document 1: Japanese Unexamined Patent Publication No. 62-66417    Patent Document 2: Japanese Unexamined Patent Publication No. 9-282642    Patent Document 3: Japanese Patent Application Laid-Open No. 2010-108583    Patent Document 4: Japanese Unexamined Patent Publication No. 2013-163667